Generally, the object of a prosthetic heart device is to assist or replace the left ventricle of a human heart. The left ventricle suffers the greatest damage in most heart cases and a replacement or aid therefor is desirable. Such devices are known by the acronym LVAD for Left Ventricle Assist Device.
The concept of providing a prosthetic heart device is not new. Many such devices exist, however, each has problems which remain, to date, unsolved. Most LVAD's fall into three general categories: pneumatic, hydraulic and electromagnetic.
Pneumatic devices use external compressors to produce high-pressure air which powers the device. The device is generally intracorporal, and the pneumatic lines pass through the body wall to connect the prosthetic device with the high-pressure air source. The problems associated with such a pneumatic LVAD include the fact that as the pneumatic lines pass through the body wall, there is a high chance of sepsis or infection since the lines pulse with each "beat" of the LVAD.
Additionally, very high pressure air is required to produce a satisfactory pulse rate and pressure in pneumatic LVADs, causing additional complications such as a high chance of valve failure. Pneumatic systems inherently include time lag as the pressure front travels through the pneumatic line. Finally, the quality of life of a patient dependent upon a pneumatic LVAD is poor because the patient is confined to a bed near the high-pressure air source.
Hydraulic LVAD's have a separate set of problems. Such LVAD's generally consist of a motor and pump blade with the pump blade in direct contact with the blood being pumped. Blood is in contact with many surfaces in the pump. Consequently, the number of blood cells damaged during pumping is high, as is the likelihood of platelet aggregation or clotting. Further, the motor's inertia may cause small twisting movements of the LVAD with each pulse, leading to additional complications or patient discomfort.
Finally, electromagnetic LVAD's have been made in many different configurations. Heretofore, those configurations have generally possessed high power requirements. In some instances, this is due to the fact that the pumping mechanism (diaphragm, etc.) lacks means by which to return to its starting position without the use of external power. Therefore, power must be supplied to move the mechanism in both directions. Power is required to pump the blood and to fill the pump chamber with blood from an auricle. These high power requirements also stem from inefficient conversion of electrical energy to magnetomotive force.